Conventional gas turbines operate at relatively high speeds. For operation of a gas turbine, absolute and relative positions of rotating and stationary parts are usually maintained within certain design tolerances. Typically, axial movement of gas turbine buckets may be restricted by a lock wire system and vertical movement may be restricted by a dovetail locking system.
However, if a lock wire moves away from its radial position, it may cause buckets to move in forward or aft axial directions. If this movement exceeds a design limit, it may cause damage to a bucket or other adjacent hardware. Such damage can result in forced outages and expensive repair or replacement of various hot gas path components.
Monitoring the health of hot gas path components can help to assess their condition, identify signs of possible failures, and allow taking appropriate failure preventive measures.
One conventional method used in monitoring axial movements of buckets includes borescope inspections. The borescope inspections enable analyzing internal machine defects and performing certain maintenance before equipment failure occurs. However, such inspections can only be performed when the gas turbine is offline.
Another conventional method includes detecting bearing vibrations that may indicate turbine bucket problems. This method, however, only allows identifying a problem when significant damage has already occurred and, thus, does not prevent damage and associated costs.